The present invention relates generally to computer printers, and pertains more particularly to the cleaning of optical components used in these printers.
Inkjet printers, and thermal inkjet printers in particular, have come into widespread use in businesses and homes because of their low cost, high print quality, and color printing capability. These printers and related hardcopy devices are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInk Jet Devices,xe2x80x9d Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988). The basics of this technology are further disclosed in various articles in several editions of the Hewlett-Packard Journal [Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994)], incorporated herein by reference.
The operation of such printers is relatively straightforward. In this regard, droplets of a colored ink are emitted onto a print medium such as paper, transparency film, textiles, and the like during a printing operation, in response to commands electronically transmitted to a printhead. These drops of ink, which are typically dye-based or pigment-based, combine on the print medium to form a pattern of spots that make up the text and images perceived by the human eye. Inkjet printers may use a number of different ink colors. One or more printheads are mounted in a print cartridge, which may either contain the supply of ink for each printhead or be connected to an ink supply located off-cartridge for the printhead. An inkjet printer frequently can accommodate two to four such print cartridges. The cartridges are typically mounted side-by-side in a carriage which, during printing, scans the cartridges back and forth above the medium, and the ink droplets are controllably ejected, at the proper times and at the proper locations of the print cartridges relative to the print medium, so as to form the printed text and images on the print medium.
Many such printers incorporate optical components within the printer housing. These components are used for many purposes, including detecting the position of the carriage within the printer, detecting the motion and position of the print medium in the printer, determining the type of print medium, determining the alignment of print cartridges in the carriage, and evaluating the quality of printed text and images on the medium. The optical components may include a light source, a light sensor, a lens assembly, or a combination of these.
During printer operation, and over time, the performance of these optical components may degrade due to the buildup of deposits on their surface. Aerosol droplets of ink intended for the print medium may instead be misdirected or carried by air currents within the printer onto the surface of optical components instead, the droplet deposits reducing the transmission of light to, from, or through the components. Other unwanted deposits, such as dust from paper print media, or debris from the external environment including dead skin, insect droppings, animal hair, carpet dirt and the like, may similarly collect on the optical components and degrade their performance. The performance degradation generally results from the deposits reducing the amount of light which can be sourced, sensed, or transmitted. Such deposits are generally not removable from the optical components by the user, and the preferred repair strategy of the printer manufacturer typically is to replace the optical component or a higher-level assembly rather than to clean the optical component.
Some printers have attempted to avoid or reduce deposits by moving the optical components away from the print medium, provide shielding around the optical components to block stray droplets, or create airflow to carry stray droplets away from optical components. However, in many cases the optical components must be located near, and with an optically unobstructed view of, the print medium in order to perform its function, and airflow management schemes are often unreliable.
Accordingly, it would be highly desirable to have a new and improved way to clean performance-degrading deposits from optical components effectively and reliably.
In a preferred embodiment, the present invention provides a cleaning system for optical components in a printer that effectively and reliably removes unwanted deposits from the surface of the components so as to automatically maintain proper operation of the printer and a high quality of printed output without requiring action by the user. By locating the cleaning system within the printer in a position which takes advantage of existing movable parts, such as the carriage of a scanning inkjet printer, the cleaning operation can be performed in a simple and cost-effective manner without requiring complex movable parts or drive components.
The cleaning system includes an optical apparatus mounted in the printer, with an optical surface on which the unwanted deposits can collect during printer operation. The optical apparatus may include one or more optical elements such as a light source (for example, a light-emitting diode or LED), an optical sensor (for example, a photocell), and a light-transmissive element (for example, a lens). Also mounted in the printer in a manner that allows for relative movement with respect to the optical apparatus is a cleaning apparatus. The cleaning apparatus is mechanically engageable with the optical apparatus during a cleaning operation of the printer so as to remove the deposits from the optical surface of the optical apparatus. The cleaning apparatus may include a scraper, a wiper, a brush, or a cleaning pad.
In inkjet printers, stray aerosol ink drops are a common source of undesirable deposits on the optical surfaces. The cleaning system preferably includes a heating apparatus for drying the deposits prior to the removing. The heating apparatus may be of any type, including a heat source and a light source. The heating apparatus is either fixed in a position, or intermittently positionable in a position, which puts it in thermal proximity to the optical apparatus so as to direct sufficient amounts of heat onto the optical surface in order to dry any wet or moist deposits. The heating apparatus may be either a source external to the optical apparatus. The heating apparatus may also be a heating element, such as a resistor or heater coil, incorporated on a surface of or within the body of the optical apparatus. In some embodiments the heating element may be fabricated into one of the optical elements, such as an LED. Such a heating element may be responsive to a separate heater control signal supplied to the optical apparatus, or to a higher-than-normal operating signal, from a print controller or other signal source in the printer. Within the printer, at least one of the optical and cleaning apparatuses is movable mounted. In an inkjet printer with a carriage that reciprocally scans from one side of the printer to the other, the movable apparatus is preferentially attached to the carriage, while the other apparatus is mounted in a stationary position to the printer frame. In such a configuration, the heating apparatus can be mounted with either the cleaning apparatus or the optical apparatus, and to either the carriage or the frame.
The present invention may also be implemented as a method for removing unwanted deposits from an optical surface of an optical apparatus in a printer. Such a method provides a cleaning apparatus within the printer for relative motion with respect to the optical apparatus. During operation, the cleaning apparatus is engaged with the surface of the optical apparatus, and the deposits are removed from the surface during the engaging. The engaging involves moving a movable cleaning apparatus into engagement with a stationary apparatus moving a movable optical apparatus into engagement with a stationary cleaning apparatus, or moving both a movable optical apparatus and a movable cleaning apparatus into engagement with each other. The removing includes scraping, wiping, or brushing the deposits from the surface of the optical apparatus with the cleaning apparatus. The method also involves heating the surface of the optical apparatus in order to eliminate any wetness or moisture from the deposits. The heating may be performed intermittently during a cleaning operation of the printer, or continuously during printing operations of the printer. The heating apparatus is also positioned in thermal proximity to the optical apparatus; it may be either stationarily mounted or intermittently positioned in such a proximity. Where the heating apparatus is stationarily mounted in proximity, it may also be fabricating as part of the optical apparatus assembly or as part of an optical element included in the optical apparatus. In some embodiments where the heating apparatus is part of an optical element, the heating includes applying a different-than-normal operating signal to the optical element in order to produce the heating.